from lxml import etree
import requests

xml = \
'<book category="CHILDREN">\
  <title lang="en">Harry Potter</title> \
  <author>J K. Rowling</author> \
  <year>2005</year> \
  <price>29.99</price> \
</book>'
tree = etree.XML(xml)

result = tree.xpath('/book/author/text()')

print(result)
/html/body/div[1]/section[4]/div/div[4]/a